Terahertz sensing has attracted numerous research activities in past decades. Due to the fact that many materials exhibit unique spectrum signatures in THz, different materials can be easily characterized in this band. Although a lot of research are focused on wideband sensing that are trying to capture fingerprint of different materials in THz, narrow band THz bio-sensing based on resonance has been pursued extensively as well since binding state of DNA can be identified through its refractive index change in THz. Traditionally, the change in DNA state from the single-stranded DNA to the double-stranded DNA molecules is investigated by tagging the target DNA with certain agents such as fluorescent ones. Although this method has widespread applications in DNA sensing, it has disadvantages such as the unwanted interference from the tagging agent and the extra preparatory steps. For biomolecule like DNA, its refractive index depends on its binding state to known probes. Therefore measurement of the change in refractive index enables the label-free direct detection and identification of genetic sequences. In M. Gagel, et al's “Integrated THz technology for label-free genetic diagnostics,” Applied Physics Letters, Vol. 80, No. 1, pp 154-156, (2002) and P. Bolivar, et al's “Label-free THz sensing of genetic sequences: Towards THz biochips',” Philos. Tran. R. Soc. London Ser. A Math, Phys. Eng. Sci., Vol. 362, pp. 323-333 (2004), integrated on-chip microstrip line resonator is employed to sense refractive index change in DNA. A split ring resonator (SRR) on a paper substrate is demonstrated to have capability to distinguish glucose solutions with different concentrations.
Generally speaking, there are two important aspects in THz DNA resonance sensing. One is to increase sensitivity of the sensor. Various high Q resonators, such as asymmetric split ring resonators (ASRs), Ω-shaped resonator, are developed to achieve this. Another aspect is to reduce the amount of sample needed to characterize it. For example a near field source is employed in W. Withayachumnankul et al's “Sub-diffraction thin-film sensing with planar terahertz metamaterials”, Optics Express, Vol. 20, No 9. 3, pp 3345-3352 (2012) to focus the energy onto a tiny spot beyond the diffraction limit, which consequently reduces the amount of sample needed.
In this disclosure, subwavelength scatterers are combined together to produce high order response that is useful to increase sensitivity of the DNA sensors. Three different sensing structures are proposed. Analysis is made based on their circuit models. Full-wave simulation results are also included to demonstrate performance of these sensors.
This section provides background information related to the present disclosure which is not necessarily prior art.